The present invention relates generally to a power unit, a power source switching apparatus, and a computer, and more particularly to a power unit provided with a battery enabled to supply a power to an external device, a power source switching apparatus provided with a plurality of batteries and enabled to supply a power to a load, and a computer that employs the power source switching apparatus.
In recent years, there have appeared portable personal computers (hereinafter xe2x80x9cportable PCsxe2x80x9d) developed in various sizes and provided with various functions so as to cope with the spread of mobile computing. For example, there are lap-top personal computers, more compact lap-top personal computers, palm-top personal computers and PDA (Personal Data Assistant) devices.
A portable PC generally has a removable battery mounted therein which allows the user to use the portable PC in an environment where no commercial power source is available, for example, in a train. Generally, a secondary battery that can be charged for repetitive use is employed as such a battery described above.
When a commercial power source is available, the user can connect an AC adapter (a device enabled to input a commercial AC voltage and output a DC voltage) to the portable PC. Consequently, the user can charge the secondary battery during operation of the portable PC.
However, because the capacity of one secondary battery is limited, the operating time of the portable PC is also limited. To extend the operating time of the portable PC, therefore, two secondary batteries are often built in the portable PC. Those two secondary batteries are referred to as the main battery and the second battery. A portable PC is started up with the power from the second battery. When the second battery is used up, the second battery is switched to the main battery, so that the portable PC can continue in operation.
Each of such portable PCs, home electric appliances, and other devices that use an AC adapter, a main battery, and a second battery as power sources is provided with a power source switching circuit for setting a charging path of the main or second battery via an AC adapter (hereinafter, referred to as the xe2x80x9ccharging pathxe2x80x9d), a discharging path used to supply a power from the main battery to an object computer (hereinafter, referred to as the xe2x80x9cdischarging pathxe2x80x9d), and another discharging path, etc. used to supply a power from the second battery to the object computer.
FIGS. 9 through 11 show block diagrams of such conventional power source switching circuits.
The block diagram of FIG. 9 shows a power source switching circuit in which each of the main battery and the second battery is provided with a protective circuit for preventing excessive discharging and excessive charging.
As shown in FIG. 9, this power source switching circuit is provided with a first serial circuit 100 located between a power line L from an AC adapter 62 to a DC-DC converter 66 and a main battery 130A and a second serial circuit 102 located between the power line L and a second battery 130B.
The first serial circuit 100 is provided with field effect transistors (hereinafter, referred to as a xe2x80x9cFETxe2x80x9d) FET1 and FET2. Just like the first serial circuit 100, the second serial circuit 102 is also provided with field effect transistors FET3 and FET4.
In FET1 and FET3 are formed internal diodes D1 and D3 in which the cathode is connected to the drain D and the anode is connected to the source S respectively. In FET2 and FET4 are formed internal diodes D2 and D4 in which the cathode is connected to the source S and the anode is connected to the drain D respectively. Those internal diodes are also sometimes referred to as parasitic diodes or body diodes.
A trickle charging circuit 140A and a trickle charging circuit 140B are provided between the power line L and the source S of FET1 and between the power line L and the source S of FET3 respectively. A quick charging circuit 142 is provided between the power line L and the drain D of FET2. The drains D of both FET2 and FET4 are connected to each other and FET 5 is provided between the junction point of those drains D and the power line L so as to prevent the quick charging circuit 142 from short-circuiting during a quick charging operation.
In the block diagram shown in FIG. 9, both of the main battery 130A and the second battery 130B are first charged by the trickle charging circuit until each battery voltage reaches a certain value, then charged rapidly by the quick charging circuit until they are fully charged. The expression xe2x80x98trickle chargingxe2x80x99 means charging at a slow rate so as to avoid damage to the subject battery. The battery capacity is almost zero during such trickle charging and is therefore too low to supply the power required for system operation.
FET5 is off while the quick charging circuit 142 charges the main battery 130A or the second battery 130B. FET5 is turned on when the trickle charging circuit 140A or 140B charges the main battery 130A or the second battery 130B or when either the main battery 130A or the second battery 130B supplies the DC power to the DC-DC converter 66.
Each of the main battery 130A and the second battery 130B is provided with a protective circuit 110A/110B configured by two FETs connected serially. The two FETs (FET6, FET7) in the protective circuit 110A are connected serially to the first serial circuit 100 in the same state of each FET in the first serial circuit. The two FETs (FET8, FET9) in the protective circuit 110B are connected serially to the second serial circuit 102 in the same state of each FET in the second serial circuit 102. Both FET6 and FET8 are used to protect the subject circuit from excessive charging and both FET7 and FET9 are used to protect the subject circuit from excessive discharging.
In the event that the power source switching circuit configured as described above is loaded with the AC adapter 62, the main battery 130A charged fully, and the second battery 130B in the empty state during a system operation, the trickle charging circuit 140B charges the second battery 130B. At this time, FET1 and FET3 are turned off and FET2 and FET4 are turned on. FET5 is also turned on.
Consequently, when the AC adapter 62 is disconnected from the system in that state and the power supply is thereby shut off, the DC-DC converter 66 receives DC power from the main battery 130A via the internal diode D1 in FET1, and also via FET2 and FET5.
An alternative arrangement is shown in FIG. 10. Serial circuits 100 and 102 are identical in configuration to those shown in FIG. 9; the first serial circuit 100 is formed in the power path from the main battery 132A to the DC-DC converter 66 and the second serial circuit 102 is formed in the power path from the second battery 132B to the DC-DC converter 66. However, the configuration in FIG. 10 differs from that shown in FIG. 9 in that the power output line from the charging circuit 68 is branched into two lines wherein one line is connected between the first serial circuit 100 and the main battery 132A via two FETs connected serially so that the cathodes of their internal diodes are connected to each other, and the other line is connected between the second serial circuit 102 and the second battery 132B via two FETs connected serially so that cathodes of their internal diodes are connected to each other. In addition, the block diagram shown in FIG. 10 is also different from the block diagram shown in FIG. 9 in that neither the main battery 132A nor the second battery 132B is provided with a protective circuit and the charging circuit for charging each battery is configured as a single charging circuit 68; it is not divided into a trickle charging circuit and a quick charging circuit. The control terminal (gate) of each FET is connected to a power path control IC 146 so that the IC 146 controls the switching (on/off) operation of each FET. The power path control IC is generally available and it is configured mostly as shown in FIG. 10.
In such a configuration, however, 8 (eight) FETs are required to completely separate the discharging path of each battery from the charging path. Therefore, the manufacturing cost becomes very high.
In order to avoid such an increase in manufacturing cost, an alternative configuration is used as shown in FIG. 11. In this configuration, a charging circuit 68 is provided at the DC-DC converter 66 side of the first and second serial circuits 100 and 102 respectively and the FET for protecting the charging circuit 68 from short-circuiting is provided between a power input terminal and a power output terminal of the charging circuit 68. A controller (not illustrated) controls the switching operation of each FET in this case.
In the configuration of FIG. 11, the AC adapter 62 is not connected to the internal circuit, and FET3, for protecting the charging circuit 68 from short-circuiting, is turned on when the main battery 132A or the second battery 132B supplies the power to the DC-DC converter 66 and FET3 is turned off when a sensor circuit (not illustrated) senses the connection of the AC adapter 62 to the internal circuit. Thereby, the AC adapter 62 is connected to the internal circuit, the AC adapter 62 supplies the power to the DC-DC converter 66 and the charging circuit 68 charges the batteries in each of the main battery 132A and the second battery 132B. While the charging circuit 68 is charging the subject batteries, FET3 protects the charging circuit 68 from short-circuiting between power input and output terminals.
In this configuration, the manufacturing cost is reduced more significantly than the configuration shown in FIG. 10, since a single path of each battery is used commonly as the discharging path and the charging path, thereby reducing the total number of FETs to five.
However, the configuration shown in FIG. 9 has a problem that the power loss of the power path becomes high and the manufacturing cost is increased, since the five FETs (the two FETs being provided in the protective circuit, the two FETs being used to switch between power sources, and one FET being used to protect the quick charging circuit from short-circuiting) are connected serially.
In order to solve this problem, the present inventor has proposed a technique for eliminating two FETs used to switch between the above power sources by making two FETs in the protective circuits function like the power switching FETs. This technique has left the following problems unsolved, however.
1. The technique cannot apply to a battery that is not provided with a protective circuit configured as shown in FIG. 9.
2. In the event that the protective circuit in one of the batteries develops trouble, the protective circuit in the other battery works so as to sometimes blow the temperature fuse (not illustrated). For example, because a large current flows in the main battery via the internal diode due to a short-circuit between batteries while one FET is switched to the other in a protective circuit so as to supply a power from both of the main battery and the second battery, the heat protective function of the main battery works so as to blow the temperature fuse in the main battery. In that case, the main battery develops trouble unfavorably even when there is no trouble actually detected in the main battery.
3. It is impossible while one battery is charged rapidly to provide trickle charging for the other battery. In such a case, the position of the power source switching circuit is not located between the trickle charging circuit and the quick charging circuit. This is why both FETs in the protective circuit in the other battery must be turned off while one battery is charged rapidly, and this disables trickle charging for the other battery.
Because the technique for replacing one power source switching FET with the other FET in a protective circuit gives rise to various problems as described above, the technique is not yet put to practical use.
On the other hand, there is a problem that because the conventional configuration shown in FIG. 11 needs three FETs for the discharging path of each battery, an additional FET is required as compared with the configuration shown in FIG. 10, and accordingly there is a power loss caused by this additional FET in each discharging path.
Under such circumstances, it is an aim of the present invention to provide a power unit, a power source switching unit, and a computer that can reduce power loss, as well as the manufacturing cost.
The power unit of the present invention is provided with a battery enabled to supply a power to an external device when connected thereto and a switch enabled to control the switching between on and off of the power from the battery to the external device.
Consequently, the switch of the power unit can be used as a power source switch for switching between discharging paths so as to supply a power from a battery to a subject computer. And, because the switch is provided in the power unit, switches can be eliminated from circuitry to which the power unit is connected. The power loss and the manufacturing cost are therefore reduced due to the eliminated switch.
The above switch may be a FET. The battery may be one of a number of different types including lithium-ion batteries, nickel-hydrogen batteries, nickel-cadmium batteries, and the like. And, the power unit of the present invention may further include switch controlling means for controlling switching between power sources with use of the above switch in response to a request from an external device.
A power source switching unit according to the present invention is provided with a plurality of such power units and a power path is provided between each battery provided in each of a plurality of the power units and a load. Each internal switch switches between supply and shut-off of the power so that the switch controlling means switches between the internal switch and the switch so as to prevent a short-circuit between batteries in case batteries for supplying a power to the load respectively are switched.
The number of the internal switches in one power path is determined by subtracting the number of switches enabled to switch between power sources from all the switches required in the power path. However, the minimum number is one.
For example, in case there are two enabled power switches (FET6 and FET7) among the switches (for example, FET6 and FET7 in FIG. 9) located in one power path and there are only two switches (FET1 and FET2) required to switch power sources in the power path as shown in the conventional configuration shown in FIG. 9, the minimum necessary internal switch is just one.
Consequently, because each switch of the power unit is used as a power source switch, the number of internal switches can be reduced according to the number of the switches employed as the power source switch, thereby both power loss and manufacturing cost can be reduced due to the reduced internal switches.
In the event that either the power unit switch or the internal switch in the power source switching unit develops trouble, a large current might possibly flow in the switching unit.
In order to avoid such a trouble, therefore, the switch controlling means should preferably provide control so as to shut off both of the internal switch and the switch when either the internal switch or the switch develops trouble. Consequently, the flow of such a large current can be suppressed, thereby improving the safety of the unit.
When both the power unit switch and the switch in the power source switching unit are field effect transistors (FET), it is possible to dispose the internal switch and the switch with the same power path so that their internal diodes are connected to each other at the same polarity. Consequently, just one switch and just one internal switch are required so as to prevent short-circuiting between batteries.
A computer according to the present invention is provided with such a power source switching unit and the load in the switching unit is a computer load. It is thus possible to reduce the number of internal switches thereby reducing the power loss and the manufacturing cost.
A power source switching unit according to another aspect of the invention is used to supply power to a load from an external power source and a plurality of batteries. The power source switching unit is provided with an external power circuit for enabling the above external power source to supply the power to the load; and a charging circuit enabled to charge at least one of a plurality of the batteries with the power from the external power circuit. The above batteries may be lithium-ion batteries, nickel-hydrogen batteries, nickel-cadmium batteries, or the like.
Furthermore, such a power source switching unit is also provided with a plurality of serial circuits, one of which is provided in each of the power paths from each of the batteries to the load. Each of the serial circuits is configured by two switches connected serially so that diodes disposed in parallel in the switches are connected to each other at the same polarity terminals. Concretely, this serial circuit is configured by two switches connected serially so that the anode or cathode of each diode is connected to that of another diode in them.
Furthermore, this power source switching unit includes a power source switching circuit configured so that a switch in which diodes are disposed in parallel is connected to the junction point between the two switches in the corresponding serial circuit and the diodes in the switch are connected to the diodes in the two switches at the same polarity terminals. The switch is provided in each power path between the charging circuit to each of the batteries.
The power source switching unit configured as described above can use one of the two switches in the serial circuit, which is located at the battery side, commonly for discharging and charging the battery. Consequently, it is possible to reduce the number of power source switching circuits, thereby the manufacturing cost can be reduced more than when the switch is not used commonly.
Furthermore, the power source switching unit configured as described above can use one of the two switches in the serial circuit, which is located at the load side, commonly for discharging the battery and preventing the charging circuit from short-circuiting while charging the battery. It is thus possible to reduce the number of the switches in the discharging path, thereby the power loss in the discharging path can be reduced more than when a dedicated switch is provided in each discharging path so as to prevent the charging circuit from short-circuiting.
A field effect transistor (FET) should preferably be employed as each switch in the power source switching unit. Because internal diodes are usually formed in parallel in a FET, these internal diodes can be disposed in parallel in such a switch, thereby simplifying the configuration of the switch.